In the near future most cochlear implant patients will hear with two 'ears' -- either with two cochlear implants (CI) or with a CI and a hearing aid in the opposite ear (combined electric and acoustic hearing or EAS). The goal of the research proposed here is to develop a tool for clinical decision making relative to these two interventions. Clinical decision making will depend critically on the nature of the tests and environments used to assess the benefit of having two ears participate in speech understanding. Standard clinical test environments can only approximate the real world environment of having sound surround the listener. Laboratory environments with multiple, spatially separated speakers can simulate real world environments but cannot be duplicated in the clinic for reasons of time, space and cost. In this project we will test EAS and bilateral CI patients in both standard and realistic test environments with the goal of creating a decision matrix that links data that can be easily collected in the clinic, e.g., CNC scores in quiet and the amount of residual hearing, with data that cannot be collected in the clinic, i.e., data collected with multiple, spatially separated loudspeakers. We propose to test bilateral CI patients and EAS patients in two realistic test environments using an 8-speaker 'surround sound system' which can simulate, with high fidelity, (i) a restaurant environment with speech babble as the noise, and (ii) a cocktail party environment with competing sentence material as the noise - a situation of 'informational' masking.